TWI389944B - Process for the preparation of an artificial latex - Google Patents

Abstract

A process for the preparation of an aqueous rubber emulsion (artificial latex), comprising the steps: (a) size reduction of the rubber, whereby granules are produces with shorter dissolving time; (b) cement formation, wherein the granules of step (a) are dissolved in a suitable hydrocarbon solvent; (c) preparation of an aqueous soap solution; (d) emulsification of the cement formed in step (b), using the aqueous soap solution prepared in step (c), thus forming an oil in water emulsion; (e) hydrocarbon solvent removal, resulting in an aqueous emulsion of the rubber, and optionally (f) emulsion concentration, forming an artificial latex with a higher solids content, characterized in that in step (a) the size reduction is carried out using a chopper and/or granulator wherein a soap is used as processing aid, preferably identical to the soap used in steps (c) and (d).

Description

Method for preparing artificial latex

The present invention relates to a method of making an emulsion of rubber in water (so-called "artificial latex"). More particularly, the invention relates to the preparation of conjugated diene polymer latexes, more particularly isoprene rubber latexes.

Both natural and synthetic rubber latexes are emulsions of rubber in water. The emulsion is stabilized by a protein or surfactant. The diameter of the rubber particles averages from 0.1 micron for some synthetic latexes to nearly 1 micron for natural latexes. The term "latex" is applied to synthetic as well as natural latex and originates from the botanical name of a milky fluid derived from a rubber tree and being a source of natural rubber. The term "slurry" is used in aqueous media.

Methods for making emulsions of rubber in water have been known for many years. For example, the following steps are known in US Pat . No. 2,595,797 : 1. Preparation of a rubbery polymer in a volatile organic solvent insoluble in water, using a solution of sufficient concentration to emulsify 2. Introducing the solution under pressure into a surfactant containing (for example , sodium sulfosuccinate dioctyl ester) in water 3. Add defoamer (for example, polyoxyl oleate) and stir the mixture until the emulsion is obtained 4. Remove the solvent by flashing (while avoiding excessive foaming) 5. Concentrate the solid content of the emulsion by allowing the emulsion to pass for 24 hours and remove the slurry (containing less than 2% solids).

Likewise, a process for the manufacture of an aqueous dispersion of an elastomer is described in US Pat . No. 2,799,662 , the method consisting of a number of integrated steps comprising drying the polymeric material in a suitable selected solvent, thus The prepared polymer solution is dispersed into a carefully selected and conditioned aqueous emulsifier system, and finally, the solvent is stripped to leave a polymer dispersion. According to this reference, in the preparation of a water emulsifier system, it is highly desirable to have two emulsifiers, one of which is of a hydrocarbon soluble type (for example, having 20 to 21 carbon atoms arranged in an alkyl-aryl structure) Alkali metal petroleum sulfonate) and one of which is a water soluble type (for example, an alkali metal sulfate derivative of a higher alcohol). Emulsification of the polymer solvent mixture and the aqueous emulsifier mixture is accomplished under conditions which prevent flashing of the solvent.

US 2,871,137 deals with the problem of emulsion stability when stripping a solvent, which provides a process for preparing an emulsifier based on the emulsified hydrocarbon polymer.

Further, a method for preparing a stable emulsion of a polymeric or resin material is described in US 2,947,715 . This is accomplished by dissolving the rubber or resin in a suitable solvent, adding an emulsifier layering agent to the polymer solution during emulsification and layering the latex emulsifiable concentrate prior to removal of the solvent, removing the solvent and then re-solving the solvent-free latex emulsifiable concentrate. Layered and completed.

In US 2,955,094 , orthophosphoric acid and an organic sulfate are used as emulsifiers in the preparation of emulsion latexes from hydrocarbon polymers. As indicated in this reference, experience has shown that latex is relatively unstable and tends to solidify when subjected to mechanical stress. Mechanical instability can be caused by the simple movement of the agitator that agitates the gel. Since the equipment becomes coated with the solidified rubber, the maintenance cost increases, and in addition, a considerable amount of rubber is lost. Another type of instability encountered with polymer latexes is that they flow out during the solvent stripping step, such as oil, and gradually form condensate.

In US 3,250,737 , it has been mentioned that synthetic elastomers produced by solution polymerization methods have received considerable attention due to technological advances and changes. This reference sets out to produce a concentrated elastomeric latex of synthetic elastomer (from its organic solution) in a fast, efficient and economical manner. This is achieved by mixing a solution of the synthetic elastomer in an organic solvent, water and an emulsifier, homogenizing the mixture at least until the resulting emulsion is stable, stripping the organic solvent at a high temperature and pressure below the water boiling condition, and centrifuging the resulting diluted aqueous solution. The latex is completed by recovering and recycling the aqueous slurry from the centrifugation step and recovering the concentrated latex. This reference focuses on the steps of flashing and centrifuging, and it is not important how the hydrocarbon solution is made.

In order to give an impression of the overall method described in the prior art, reference is made to the method described in Chapter 9 of Stanford Research Institute. PEP Report No. 82. SRI, 1972. Thus, a premixed tank is fed a solution of polyisoprene in isopentane which is premixed with the soap solution (mostly slurry recycle) from the slurry storage unit in the tank. The mixture is fed into an emulsification loop wherein the ratio of recycle to fresh feed is about 2/1. The emulsifier is a high speed (3,500 rpm) centrifugal pump. The emulsion was passed to a storage tank where the emulsion was stored for 3 hours, allowing any "cream" (emulsion with oversized particles) to rise to the top and be recycled. Thus about 1% of the emulsion is recycled to ensure any slight amount of complete emulsification that was not previously fully emulsified. If any portion of the emulsified concrete is in the form of oversized particles when flashing or stripping the solvent therefrom, the resulting polymer will not remain in the colloidal suspension, but will deposit and contaminate the equipment. From the storage tank, the emulsion passes to the heater where a substantial portion of the solvent (but only a small portion of the water) evaporates into gas bubbles, causing the formation of a foam like foam. The foam passes to the time slot to allow the solvent to reach its equilibrium concentration relative to the polymer throughout the foam. The foam was then cooled to 110 °F at about 10 psig to allow the solvent to concentrate and the foam to burst. The concentrated solvent forms a separate liquid phase from the aqueous emulsion phase. The mixture is passed to the separator via a coalescer packaged by steel wool. The separated solvent is transferred to a solvent buffer tank. The emulsion is centrifuged and concentrated in a centrifuge where a quantity of slurry is separated and recycled to the slurry storage tank. Since the polymeric particles in the concentrated emulsion still contain a solvent, the emulsion is passed through the second stage of foam formation, cracking and phase separation. The second stage separated solvent is also transferred to a solvent buffer tank. The second stage emulsion phase was heated to 180 °F in a flash heater to flash off the remaining solvent in the flash tank. This solvent was concentrated and stored in a solvent buffer tank. Some of the water is also flashed from the flash tank and concentrated, separated, and recycled to the soap solution tank. The latex from the flash tank contains about 24% rubber solids. It was cooled to 110 °F in an emulsion cooler, concentrated to 64% in a centrifuge and finally collected and stored in a latex product storage container. The slurry spun out during the concentration step is recycled to the slurry storage vessel.

An invention is described in GB 1295250 relating to the manufacture of a solvent dispersion comprising a crystal lattice from a high polymer composition. This method involves the removal of solvent via extended and progressive stripping. At the beginning of the process, in high-polymers such as rubber grinders, Banburry or the like, high-polymers, such as high-temperature and/or high-shear polymer materials and such as Or non-reinforcing fillers, softeners, oil gels and other processing aids are carefully studied to achieve the desired treatment viscosity. Thus, it appears that the method of this reference introduces foreign materials into the polymer. In addition, the result of the fine study is a decrease in the average molecular weight, that is, a decrease in the decrease in viscosity. The method for granulating the polymer while leaving the molecular weight intact is not disclosed.

A process for the manufacture of emulsions, crystal lattices and foams based on cis-1,4-polyisoprene is described in GB 893066 . This reference describes a procedure for the manufacture of cis-1,4-polyisoprene as solid crumbs and the introduction of emulsions and crystal lattices of cis-1,4-polyisoprene from solution polymerization systems. Polyisoprene which may actually have a cis-1,4-content of from about 85 to 97% or more than 97% can be prepared by any known solution polymerization method carried out in an inert diluent, wherein polymerization is carried out. At the end of the time, the obtained polymer is contained in a solution in a diluent. This reference provides a detailed description of the emulsification procedure in which a solution of the polymer is used. This reference does not describe the preparation of the solution from dry polyisoprene.

US 3310515 relates to the preparation of an organic solvent solution for a crystal lattice from an elastomer. Synthetic latex is very useful in the manufacture of foam rubber or honeycomb products. In the conventional procedure for preparing latex from a polymer solution, the main objective is to prepare anti-coagulant formation during the processing steps of formation, vaporization and concentration (although not sufficiently stable to be modified into a gel to form a continuous sponge or thinner Sewing shape) of latex. The invention provides a method for preparing a crystal lattice of a synthetic elastomer having an average particle size in a range necessary for sufficient stability and at the same time being suitable for concentration by any of several means, Equivalent methods include emulsification and subsequent treatment of the elastomeric coagulum to obtain a latex of the elastomer in an aqueous medium. The solid form of the elastomer can be dissolved or redissolved, but how it is done is not disclosed.

Interestingly, the step of dissolving the dried polymeric material in a suitable solvent is not generally described in detail, and this step may be a bottleneck and/or further cause during processing and/or in the manufacture of a hydrocarbon polymer organic solvent solution. The problem in latex.

Therefore, smaller particles (larger surface area) are more common in dissolving the larger particles. Isoprene rubber (hereinafter "IR") and similar hydrocarbon polymers are generally sold and shipped in packages. In order to dissolve the IR in an organic solvent more quickly, it will be apparent that the chopped and/or granulated hydrocarbon polymer.

For example, GB 983297 relates to a process for producing an aqueous dispersion of a diene polymer material by forming a solution of a polymer in a water immiscible solvent, adding an emulsifier, and forming an emulsion forming a mixture. And prepared by removing the solvent from the emulsion. In Example 1, cis-1,4-polyisoprene cutting / chopping of _^3/4-thick sheet of _^"1/4 by square." This reference does not disclose the cutting and/or shredding step itself. On the other hand, IR and similar rubber materials are difficult to shred and/or granulate and also have a tendency to re-agglomerate (due to cold flow) if there is any form of transport or storage prior to the dissolution step. Therefore, there remains a need to further improve the methods of the prior art. Similar conclusions can be drawn based on US 5792494, which only describes a solid elastomer that is reduced in size to less than 5 centimeters (eg, by comminution). How this is done effectively and without the introduction of non-blocking and/or foreign materials is not discussed.

The use of anti-adhesives such as talc or zinc stearate, etc., is common to prevent agglomeration of polymeric particles. On the other hand, it is highly undesirable to have foreign materials in the resulting latex. In fact, materials in any form should be avoided in the preparation of seamless articles such as medical gloves and condoms and the like. Therefore, the use of talc is not recommended.

It is an object of the present invention to provide an improved process for preparing a hydrocarbon polymer organic solvent solution for use in preparing a polymer latex. Another object of the present invention is to provide an improved method of making a polymer latex.

It is therefore clear that methods for preparing artificial latex without being affected by the aforementioned drawbacks are still of interest. Modifications to the methods are provided below, each of which is independent, but in particular substantially improves the feasibility of the preparation process when combined, while maintaining the high quality of the artificial latex produced.

A method for preparing an aqueous rubber emulsion (artificial latex) comprising the steps of: (a) reducing the size of the rubber, thereby producing the particles in a shorter dissolution time; (b) forming a concrete, wherein the step (a) is The particles are dissolved in a suitable hydrocarbon solvent; (c) preparing an aqueous soap solution; (d) emulsifying the concrete formed in step (b) using the aqueous soap solution prepared in step (c), thereby forming an oil-in-water Emulsion; (e) removing the hydrocarbon solvent, obtaining an aqueous emulsion of the rubber, and optionally (f) concentrating the emulsion to form an artificial latex having a higher solid content, wherein in step (a), by using a chopper The size reduction is performed by a granulator and is characterized by the use of soap as a processing aid, preferably the same as the soap used in steps (c) and (d).

The soaps used in steps (c) and (d) are the same.

Mode for carrying out the invention

The rubber used to form the artificial latex can be any polymer known in the art which is typically produced by solvent polymerization. This includes, for example, polyisobutylene and copolymers thereof, polyvinyl compounds such as acrylic acid and methacrylic acid esters, and polyvinyl ether and also cellulose derivatives, copolymers of styrene and conjugated dienes and/or acrylonitrile, and A polymer (copolymer) of a diene. Another class of polymers are copolymers prepared from ethyl and a monoolefin having up to 8 carbon atoms, such as an elastomeric copolymer of ethyl and propylene, and a copolymer of ethyl and butane-1. And its analogues. Another class of rubbery polymers is a terpolymer obtained from ethylene, propylene, and a diene such as 1,5-hexadiene and the like.

Polydiene polymers (copolymers) have received particular attention, with butadiene and isoprene being representative of dienes. Preferably, the polymers (copolymers) are polymerized to a higher cis-1,4-content (at least about 90%) by solution polymerization. These polymers (copolymers) are further characterized by a (very) high molecular weight. Most preferably, it is produced by anionic polymerization in the presence of a lithium catalyst rather than a Ziegler-type catalyst, thus ensuring a very low ash content. Most preferably, the rubbery polymer is an isoprene rubber, such as any of the varieties marketed by KRATON Polymers.

The method of the present invention can also be applied to the case of producing an artificial latex using a natural rubber bag.

The rubbery polymer (preferably isoprene rubber) can be dissolved in any suitable solvent. Regarding the solvent to be selected, the choice depends on the exact nature of the rubber and the boiling point of the solvent itself. It is necessary to use a solvent which dissolves the rubber quickly (and easily). For less polar polymers, aliphatic hydrocarbon solvents having from four up to about ten carbon atoms are useful. These include isopentane, cyclopentane, n-pentane, hexane, heptane, octane and the like. For the isoprene rubber, the preferred solvent is n-pentane.

The normal limit on the amount of rubbery polymer dissolved in the solvent will be the range of solubility of the polymer in the solvent. In the case of isoprene rubber, a preferred concentration is less than 20% by weight, preferably 10-15% by weight of solids. Another way of defining the amount of rubbery polymer is by viscosity of the polymer solution, which should preferably be less than 20,000 centipoise (at 25 ° C).

For the reduction in the size of the rubber bag, a shredder and/or a granulator can be used regardless of the natural or synthetic rubber. Preferably, the use of a shredder and/or a granulator in one or two steps of preparation reduces the rubber from standard bag size to less than 50 mm, preferably less than 25 mm, more preferably less than 15 mm. Average particle size. An average particle size of less than about 5 mm generally does not provide an additional advantage.

There are no specific conditions for this preliminary step. It is obvious that the safety conditions imposed by the equipment manufacturer must be followed and the degradation of the rubber must be avoided.

Any soap can be used in principle. However, since the potential problem of the present invention is to avoid foreign materials that limit the use of the latex thus produced, the soap is preferably approved for use in foods and skin. It is preferably equivalent to the soap used in the subsequent steps (c) and (d). For the preparation of IR latex, rosin type soap is preferably used.

Preferably, soap is used in water at a concentration between 0.5 and 5% by weight. Larger concentrations of solutions can be used, but generally do not provide an advantage. At this point it is noted that the hardness of the water used in the preparation of the soap solution is important. For the preparation of soap solutions, strong soft water (0-4 DH) or soft water (4-8 DH) should be used.

The amount of soap to be used during step (a) will depend on the equipment used in the size reduction step. Sufficient soap should be used to avoid re-agglomeration in the chopper and/or granulator or after a short period of time. Excess soap can be recycled. In other words, the amount of soap is not critical and is fairly easy to determine for those skilled in the art. A good starting point is that the weight ratio of soap solution to rubber is from 3:1 to 1:3, preferably from 1:2 to 2:2.

After making the smaller particles of rubber the starting material, it can be dissolved in the solvent by any conventional means. For example, it can be dissolved in a solvent (below its boiling temperature) in a stirred tank.

Latex can be made by any of the methods known in the art. This includes each of the prior art references referred to in the paragraphs [0003] to [0015], which are hereby incorporated by reference, and also incorporated herein by reference in its entirety by reference in its entirety, in its entirety, in its entirety, ln. US 3,261,792; US 3,268, 051; US 3, 307, 777; US 3, 281 386; US 3,287, 301; US 3, 285, 869; US 3, 305, 508; US 3, 315, 151; US 3, 315, 516; US 3, 313, s, s, s, s, s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s s FR2153913; GB1296107; FR2172455; US3815655; US3839258; US3842052; GB1384591; US3879326; US3892698; US3862078; US3879327; US3886109; US3920601; JP51080344; JP50127950; JP54124042; JP54124040; US4243566; JP56161424; US4344859; SU1014834; JP58091702; SU1375629; JP1123834; And RO102665; and US3007852; US3622127; US4160726; GB2051086; JP58147406; SU1058974; EP512736; JP8120124 and US6075073.

The following examples will further illustrate the invention in further detail, but are not intended to limit the invention in any way.

Example 1

Several size reduction tests are performed using a combination of devices (eg, a chopper and grinder) or a single machine (eg, a granulator). Very good results were obtained using a granulator.

The IR package (approx. 34 kg) and the halved size package were used for testing using a rotor and stator knife equipped with a feed chute, a cutter and a screen with a suitable grid size (less than 25 mm). Granulation machine.

The anti-adhesive can be used to granulate the IR package with almost no clogging. However, clogging occurs when the anti-adhesive agent is not used. The use of a concentration of 1.5% by weight of rosin-type soap (prepared in demineralized water) at a ratio of about 3 kg of soap to 5 kg of rubber results in an excellent yield, wherein the rubber particles have an average size of less than 25 mm.

Claims (3)

A method of preparing an aqueous rubber emulsion, comprising the steps of: (a) reducing the size of the rubber, thereby producing the particles in a shorter dissolution time; (b) forming a concrete in which the particles of the step (a) are dissolved In a suitable hydrocarbon solvent; (c) preparing an aqueous soap solution; (d) emulsifying the concrete formed in step (b) by using the aqueous soap solution prepared in the step (c), thereby forming an oil-in-water emulsion (e) removing the hydrocarbon solvent, obtaining an aqueous emulsion of the rubber, and optionally (f) concentrating the emulsion to form an artificial latex having a higher solid content, wherein in step (a), the reduction is by Executed using a chopper and/or a granulator, characterized in that soap is used as a processing aid. A method of preparing an aqueous rubber emulsion according to claim 1, wherein the soap used as a processing aid is the same as the soap used in the steps (c) and (d). A method of preparing an aqueous rubber emulsion according to claim 1 or 2, wherein the rubber is isoprene rubber and the soap is a rosin type soap.